Lambda settings explained

You may have heard people talking about the lambda setting of their engine but not paid it much attention. You may have wondered what it meant and looked on the internet only to be drowned in technical jargon. I thought I would jot down some of the key points to explain what it means!
The lambda reading is a very useful thing to know. It tells you how lean or rich your engine is running at a split second in time. Armed with this information, you can either tell your mates, make some changes to the engine to change it or proudly tell everybody that it’s just right.
But what is the right setting? Firstly, we need to know what the number is found. You can’t measure lambda directly, it can only be calculated. What is measured is the air/fuel ratio (AFR) by using a probe in the exhaust gasses. This number is then divided by the theoretical ideal AFR (14.7:1, meaning that there are 14.7grams of air for every gram of fuel going in to the engine).
If your engine has an AFR of 12:1 then your lambda is 12 / 14.7 = 0.82
If your engine has an AFR of 14.7:1 then your lambda is 14.7 / 14.7 = 1
From this we can see that if the lambda is less than 1 the engine is running rich, whilst over 1 it is running lean. You could, of course, ignore lambda all together and just talk in terms of AFR, but it’s quite a cumbersome phrase.
Talking in terms of lambda largely came about when computers started to be used to run engines as it’s a much easier number for a computer to deal with.
In my next posting I’ll run through some actual examples of lambda readings from vintage cars and how they indicate what changes to make!

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